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Knowing FCP Euro warranty, I bought the aux battery from them about 4 years ago.
Than last year I measured it at lower performance, so get a free replacement.
Than I am buying Mighty Max batteries for my gates and they last 4-5 years on very cheap charger.
If you can't make your mind, flip the coin.
I'm getting the "Auxiliary Battery Malfunction" since Saturday. Stop "Hold" function is disabled.
I've recharged main battery to "floating" -- it recharges Aux. Battery, too, yes? -- then used the IcarSoft 3.0 to run codes. Got a CGW[ZGW] Central Gateway fault. I reset this code successfully, and the Malfunction Message goes away and Stop "Hold" resumes working. Unfortunately, the message returns after one drive cycle. (One drive was 4 miles, and the last drive cycle was 24 miles in length.)
I haven't tried charging the Aux. Battery separately. I assume to do this that I remove the battery, but I am reluctant to do this, for some reason...
So, should I go ahead and buy a replacement Aux Battery and hope that solves it?
FCPEuro price ($160) is $10 higher than the MB Dealer, LOL.
I'm tempted to try Krzysztof's suggested Amazon Battery noted in Post #6 above.
Any suggestions?
How old is your ECO AGM AUX Batt ?
How many odometer miles?
Is this AUX replacement: timely or premature ??
How would you say is your car doing with MAIN battery replacement: timely/premature?
Normally AUX has a good extended life.
It hardly ever does anything unless ECO is actively used or MAIN is run low.
When that happens the MOSFET reverse diode puts AUX to contribution as needed. It is recharged with a big unlimited current punch by ALT/Main.
Thus you want AUX discharged as little as possible to minimize surging of your chassis.
Last edited by CaliBenzDriver; Dec 12, 2023 at 07:43 PM.
Reason: killer surges
How would you say is your car doing with MAIN battery replacement: timely/premature?
Normally AUX has a good extended life.
It hardly ever does anything unless ECO is actively used or MAIN is run low.
When that happens the MOSFET reverse diode puts AUX to contribution as needed. It is recharged with a big unlimited current punch by ALT/Main.
Thus you want AUX discharged as little as possible to minimize surging of your chassis.
My car has 42,000 miles on it, 25,000 since I bought it. The original main battery was replaced by the previous owner in Jan, 2018 (CarFax note, before I bought it) and again in late 2019 by me under warranty. I have no idea how old the AUX is... I presume it could be new since put in service Oct, 2015.
My car has 42,000 miles on it, 25,000 since I bought it.
The original main battery was replaced by the previous owner in Jan, 2018 (CarFax note, before I bought it) and again in late 2019 by me under warranty.
I have no idea how old the AUX is... I presume it could be new since put in service Oct, 2015.
If we don't know how old AUX is and it needs one then the only thing to do is replace it.
+++ scanner reading...
I think under the F-SAM you can read the vitals of AUX: Internall resistance and voltage.
Last edited by CaliBenzDriver; Dec 12, 2023 at 08:41 PM.
Reason: SAM
I'm getting the "Auxiliary Battery Malfunction" since Saturday. Stop "Hold" function is disabled.
I've recharged main battery to "floating" -- it recharges Aux. Battery, too, yes? -- then used the IcarSoft 3.0 to run codes. Got a CGW[ZGW] Central Gateway fault. I reset this code successfully, and the Malfunction Message goes away and Stop "Hold" resumes working. Unfortunately, the message returns after one drive cycle. (One drive was 4 miles, and the last drive cycle was 24 miles in length.)
I haven't tried charging the Aux. Battery separately. I assume to do this that I remove the battery, but I am reluctant to do this, for some reason...
So, should I go ahead and buy a replacement Aux Battery and hope that solves it?
FCPEuro price ($160) is $10 higher than the MB Dealer, LOL.
I'm tempted to try Krzysztof's suggested Amazon Battery noted in Post #6 above.
Any suggestions?
My experience with the Aux Battery :
ECO Start / Stop never activated or turned on no matter how many mileage I put on the car since I bought it . Well, I hit the dealer and they said half way of the battery life span left . Well, I decided to replace both batteries main and aux . Since replacement not only the car starts better but also ECO start stop system runs effectively .
I on other hand love the ECO stops. We do have 5 miles of 45 mph streets to get to the freeway and quite often sit for 2 minutes at red light.
When ECO doesn't engage, I am getting annoyed with vibration the diesel still makes.
My GLE makes ECO stops for only 30 seconds and than will restart the engine. ANNOYING.
Thinking of buying this battery locally from Batteries Plus. There is a $20 rebate to order on line and pick up in store. This way, I can have them check the old battery to be sure it's gone bad, too.
If you have advanced charger, you can remove the battery from the car and run desulfating cycle on it.
It did restore my smaller aux battery in GLE, who after sitting for 7 months went down to 6V and car no longer wanted to recharge it.
6 months later it still works.
BUT, I just drove 50 miles with lots of stoplights. "HOLD" function is back reliably, and there is no "Aux. Battery Malfunction" warning. Go figure...
I guess I will wait until warnings return.
So AUX battery likely not the cause but a consequence.... unless it is passed due.
I believe your car has a voltage issue that stressing your AUX battery, normally lazy standby job.
#1 for that is MAIN being drained. When main is low AUX has to supply his VIP then gets punched charged.
We don't want AUX to work! It normally does not even during an ECO off (only during the crank for 5s).
Last edited by CaliBenzDriver; Dec 15, 2023 at 09:16 PM.
I'm going to jump on this axillary battery bandwagon with my issue. I replaced my aux battery about 4 months ago with an OEM from FCP Euro, and I have recently started getting intermittent malfunction warnings in the dash. I replaced the battery as a preventative measure as it was still the original battery and was nearly 8 years old. I checked the voltage and it read 12.86v which seems pretty normal, but now as I type I realize that I tested in-car and maybe it's being supplemented by the main battery. I've been super busy with work so I haven't had time to see if I could find anything with my icarsoft MB scanner. I did put my ctek charger on it for a bit but being already at a good voltage it basically jumped right over to full. I'm thinking of rolling the dice and getting another from FCP Euro and then pay to mail this one back for store credit. Thoughts?
I'm going to jump on this axillary battery bandwagon with my issue. I replaced my aux battery about 4 months ago with an OEM from FCP Euro, and I have recently started getting intermittent malfunction warnings in the dash. I replaced the battery as a preventative measure as it was still the original battery and was nearly 8 years old. I checked the voltage and it read 12.86v which seems pretty normal, but now as I type I realize that I tested in-car and maybe it's being supplemented by the main battery. I've been super busy with work so I haven't had time to see if I could find anything with my icarsoft MB scanner. I did put my ctek charger on it for a bit but being already at a good voltage it basically jumped right over to full. I'm thinking of rolling the dice and getting another from FCP Euro and then pay to mail this one back for store credit. Thoughts?
These cars should not have an appetite to eat any Main/Aux battery.
Take this opportunity to find the root cause:
-1- clean ypu main chassis strap
-2- Asses engine voltage
What's guaranteed to workout your Aux dead is yoyo on Main.
When Main voltage stays up Aux does not need to contribute.
Last edited by CaliBenzDriver; Dec 20, 2023 at 06:06 PM.
Judging battery from static voltage is not telling much (unless battery is dead).
You need to load-test it.
When MB is pretty mysterious about telling owners how exactly the system work, common knowledge is that aux battery is disconnected from main system when ignition is off.
... common knowledge is that aux battery is disconnected from main system when ignition is off.
I've read on these forums in several threads that charging the main battery also charges the Aux. So, how does recharging the main battery while ignition is off also recharge the AUX?
I've read on these forums in several threads that charging the main battery also charges the Aux. So, how does recharging the main battery while ignition is off also recharge the AUX?
W212 if 1st MB I own, who is using aux battery for ECO restarts.
Previous models, as well as my GLE do have smaller batteries as a backup for either SBC brakes, or electric gear shifter and those are charged only for short time on vehicle restart and then the module completely disconnects them from the vehicle till the emergency strikes.
Obviously ECO battery is working in the system at least most of the time, but I could never find good info how it operates. Manu fact even info what it does is very sketchy and when some says it powers transmission pump, the other say it keeps the headlights bright.
My GLE does it all without big aux battery, although ECO stop is limited to 30 seconds.
the electrical system uses full featured state of the art design with a little bit of troubles sprinkled here and there to keep businesses busy You're not going to understand all in one read.
Batteries die from deep cycling and abuse.
AUX has a poor charging control. It has no charging sensor... just like the engine oil pressure: no sensor!
ECU is 100% clueless about AUX charge discharge status. R-SAM only tests for dead/alive internal resistance.
So knowing what we have, what can be done?
Once your MAIN circuit is good, then AUX will have a normal life.
SIMPLY ADD A SECONDARY GND STRAP conveniently left out unlike with Japanese cars.
This will cancel all battery chaos and disrupted electronic modules - Happy ownership & Merry Xmas to friends.
+++ INCENTIVES :
GND Strap is also #1 STARTER killer with abnormally high current, slow cranks.
Last edited by CaliBenzDriver; Dec 20, 2023 at 08:27 PM.
Reason: starter ender
Can you show us pictures of what you added and supply part #'s ? Thanks
You need a second GND Strap mounted high-up to stay dry/clean between (engine <-> chasis).
Here what my version looks like: secondary GND
My version is not the best possible! Others can do better given engine, supplies....
The best straps are the shortest, mine can be improved with a 3rd strap. All straps share the resistance to minimize drop voltage of high currents.
Cleaning existing requires access to under carriage area... this will do great but short lived because of it's worst exposure factor.
W212 MY'14: worst strap location....
This fits the bill for being short but exposed to road grime and heat cycles!!
This factory strap is tied to engine/tranny bell housing bolt.
> Additional strap locations:
2x close by locations
between engine - chassis
big size nut
a nonessential nut (Not: strut mount!)
good chunky steel (not fake firewall skirt!)
this is to conduct part of 800Amps!!
Put in a 3rd strap is a perfectly good way to split dynamic current and reduce drop voltage spikes.
Aluminum is known to develop an insulating oxide unlike steel rust is a conductor. Meaning prefer connecting to steel parts... these mordern engine have no steel. This forces us to deploy multiple aluminum straps... Multiples are the best solution.
Last edited by CaliBenzDriver; Dec 22, 2023 at 05:34 PM.
Reason: not a simple cake walk!!
2016 E350 4Matic wagon, 2019 Ford Expedition, 2019 Chevy Bolt EV
from what I understand, the main thing the Aux battery does is keep all the car electronics running when the starter motor is engaged. traditionally cars had a 'load shed relay' that kills everything extra when you engage the starter, this turns off the headlights, the air conditioning compressor and fan, the stereo, etc. On a heavily computerized car like the W212, all those computers would have to reboot if they did it that way, so instead, the 'load shed' moves those loads to the aux battery.
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